Anatomical, physiological and behavioral studies will be carried out on the peripheral auditory system of bats of the family Mormoopidae, in particular Pteronotus parnellii. The ears of these bats are especially sensitive to sounds in a narrow frequency band. We plan to use a pendulum device where the animals, velocity and position can be accurately determined in order to make detailed analyses of pulse and echo evoked responses. Both cochlear microphonic and evoked neural potentials will be examined in relation to emitted signals and echoes and in relation to fluttering targets which mimic insect wing beats. Morphological studies will be directed to specializations of the cochlea in the regions responding to 59-63 kHz. We plan to continue using trypsin digested material in the SEM and to study serial sections and computerized reconstructions in a systematic way in order to characterize the structures and structural relationships. Ultrastructural features to be examined include the unusual gelatinous lining of the scala tympani, the supporting cells of the organ of Corti and the occurrence of contractile proteins in the ear. The cochlea of Pteronotus parnellii will be compared with other mormoopids whose ears appear to be much less specialized for fine frequency resolution.